How do I calculate the solid angle formed by three vectors?

[Jhenrique]

How I do for calculate the solid angle formed by 3 vectors like:
http://s30.postimg.org/61lpvmi4h/solid.jpg
?

 

[chogg]

Googling for "solid angle 3 vectors" gives this result, which looks useful:
http://math.stackexchange.com/questions/202261/solid-angle-between-vectors-in-n-dimensional-space

 

[Jhenrique]

Rox! under my nose and I didn't see!